1. Field of the Invention
The present invention relates to refrigerator oil compositions and fluid compositions for refrigerators, said fluid compositions each being a mixture of the refrigerator oil composition and a refrigerant, and more specifically to refrigerator oil compositions and fluid compositions which are suitable for use in compression refrigerators operated using a fluoroalkane refrigerant and have excellent lubricating property.
2. Description of the Related Art
As lubricating oils for refrigerators cooled using a Cl-containing refrigerant such as CFC-12 or HCFC-22, there have been known lubricating oils containing, in addition to a base oil such as a mineral oil, alkylbenzene or a mixture thereof, a phosphate ester and/or a phosphite ester (Japanese Patent Laid-Open No. 91502/1979), trioleyl phosphate (Japanese Patent Laid-Open No. 86506/1976), a phosphite ester (Japanese Patent Laid-Open No. 139608/1979), tricresyl phosphate and/or triphenyl phosphite (Japanese Patent Laid-Open No. 27372/1980), a phosphate ester and a hydrogen phosphite ester (Japanese Patent Laid-Open No. 92799/1980), an organomolybdenum compound and an acid phosphate ester (Japanese Patent Laid-Open No. 75995/1984) or a thiophosphate (Japanese Patent Laid-Open No.293286/1986).
The lubricating oils containing a phosphite ester therein, however, have the drawback that the phosphite ester reacts with water remaining in or penetrated in a refrigerator system and forms phosphoric acid, thereby corroding metals in the system.
The lubricating oils containing a thiophosphate therein also have the drawback that thermal decomposition products of the thiophosphate corrode copper pipes in a system, windings of a motor in a hermetic-type compressor, and the like.
Such conventional additives are employed in combination with a Cl-containing refrigerant such as CFC-11, CFC-12, CFC-115 or HCFC-22. As have already been reported by Honma et al. in the Preprint D.9 (1989) of the 34-th National Meeting of Japan Society of Lubrication Engineers, chlorine atoms chemically bound with a refrigerant molecule in a large amount in the system act as an extreme pressure additive so that their function as extreme pressure additives are not particularly important. In spite of the drawbacks described above, the addition of a phosphate ester, phosphite ester, acid phosphate ester or hydrogen phosphite ester alone is sufficient for the lubricating property.
In the case of a compression refrigerator operated using a fluoroalkane refrigerant, which is a substitute for CFC refrigerants, said refrigerants being subjected to control as they are considered to lead to destruction of the ozone layer, the situation is different. Phosphate ester additives which have heretofore been effective for mineral-oil-type refrigerator oils do not show sufficient abrasion resistance when used for refrigerator oils containing a fluoroalkane refrigerant because of the following reasons:
Fluoroalkane refrigerants containing no chlorine atom or atoms in their molecules, such as HFC-32, HFC-125, HFC-134a and HFC-152a, however, have no effects as an extreme pressure additive.
Refrigerator oils for a fluoroalkane refrigerant employ a base oil having strong polarity such as oxygen-containing synthetic oils, ex. a carboxylate ester oil, polyglycol oil or carbonate ester oil, in view of their miscibility with the refrigerant so that the effects of the extreme pressure additive so added are lowered.
For weight reduction and energy saving, aluminum alloys (hereinafter called "aluminum" for the sake of brevity) have come to be used frequently for the sliding parts of the compressors of recent automobile air-conditioning systems. Although there have appeared iron-aluminum or aluminum-aluminum sliding parts accompanied with such a tendency, extreme pressure additives suitable for them have not yet been studied sufficiently.